This disclosure relates to electrode materials for electric lamps and methods of manufacture thereof.
The standard electron emissive coating currently used in a majority of electrodes of commercial fluorescent lamps contains a mixture of barium, calcium, and strontium oxides (“triple oxide emissive mixture”). Since these oxides are highly sensitive to ambient carbon dioxide and water, they are generally placed on the lamp electrodes initially as a wet mixture suspension of barium, calcium and strontium carbonates containing a binder and a solvent. The wet mixture suspension is then “activated” inside the lamp assembly during the manufacturing process by resistively heating the electrodes until the carbonates decompose, releasing carbon dioxide and some carbon monoxide, and leaving behind a triple oxide emissive mixture on the electrode.
However, the triple oxide emissive mixture suffers from several drawbacks. First, the “activation” requires an undesirably high temperature to convert the carbonates to oxides. The conversion of the carbonates to oxides undesirably releases volatile organics, carbon dioxide and some carbon monoxide. Additionally, lamps having electrodes coated with the triple oxide emissive mixture have a rather short operating lifetime. It is therefore desirable to have electrodes coated with an electron emissive mixture, which are more robust and have a longer life cycle.